1. Field of the Invention
The present invention relates to a novel non-aqueous battery. More particularly, the present invention is concerned with a non-aqueous battery comprising (1) a casing, (2) a non-aqueous electrolyte contained in a space defined by an inner wall of the casing, and (3) a spirally wound electrode assembly accommodated in the above-mentioned space, operatively with the non-aqueous electrolyte, wherein the spirally wound electrode assembly comprises a cathode (comprising a cathode active material layer), an anode (comprising an anode active material layer) and a separator which are spirally wound together into a spirally wound structure so that the cathode active material layer and the anode active material layer are arranged opposite to each other through the separator, and wherein the battery has a cathode-equipotential metallic segment provided in association with the cathode, in which the cathode-equipotential metallic segment has on at least one side thereof a portion free of a cathode active material layer to provide a cathode-equipotential, exposed metallic portion (.alpha.) longitudinally extending over a length of one wind or more of the spirally wound structure, wherein the cathode-equipotential, exposed metallic portion (.alpha.) Is positioned opposite to an anode-equipotential, exposed metallic portion (.beta.) which is provided, in association with the anode, over a length of one wind or more of the spirally wound structure. The present invention is also concerned with a non-aqueous battery having substantially the same construction as in the above-mentioned battery, except that, in place of the above-mentioned spirally wound electrode assembly, use is made of a stacked laminate electrode assembly or a zigzag-folded laminate electrode assembly, each having substantially the same cathode/separator/anode structure as that of the above-mentioned spirally wound electrode assembly. By virtue of the above-mentioned unique construction of the battery of the present invention, it has become possible to ensure the safety of the battery even when the battery suffers an accident. Specifically, even when the battery of the present invention suffers accidents, such as an accident In which the battery casing is crushed by an external pressure, an accident in which the battery is overcharged by a malfunctioning of a charging circuit or the like, an accident in which the battery is penetrated with a metallic nail or the like, and an accident in which the battery is exposed to heat from an external high-temperature heat source, the battery is adapted to be easily subject to short-circuiting between metallic segments having very low electric resistance, to thereby prevent the occurrence of a rapid temperature elevation in the battery, so that the safety of the battery can be ensured.
2. Prior Art
A conventional lithium ton secondary battery using a non-aqueous electrolytic liquid generally has a construction in which a spirally wound electrode assembly is used, wherein the electrode assembly comprises a cathode sheet (prepared by coating an aluminum foil with a lithium-containing composite metal oxide as a cathode active material), an anode sheet (prepared by coating a copper foil with a carbonaceous material as an anode active material) and a separator composed of a microporous polyethylene film or the like (which is disposed between the cathode sheet and the anode sheet) which are spirally wound together into a spirally wound structure, and in which the electrode assembly is accommodated In a can made of stainless steel, which functions as an outside electrode, such as an outside anode. With respect to the details of the above-mentioned lithium ion secondary battery using a non-aqueous electrolytic liquid, reference can be made, for example, to Unexamined Japanese Patent Application Laid-Open Specification No. 2-51875 and Unexamined Japanese Patent Application Laid-Open Specification No. 5-234620.
The above-mentioned lithium ion secondary battery has various advantageous characteristics, such as high capacity, high voltage and high output. However, due to the above-mentioned characteristics of the lithium ion secondary battery, it is important to ensure the safety of the battery as described below in detail. For the purpose of ensuring the safety of the lithium ion secondary battery, it has conventionally been practiced to provide a lithium ion secondary battery having various types of protective means, such as a temperature fuse, a current fuse and a PTC element, so as to prevent occurrence of the temperature elevation at an accident, such as an accident in which a short-circuiting between the cathode and the anode occurs due to a malfunctioning of the circuit or the like. Further, it has also conventionally been practiced to provide a lithium ion secondary battery having a safety valve so as to prevent occurrence of the elevation of the internal pressure of the battery.
However, it is possible that the short-circuiting of the battery occurs at various accidents other than the above-mentioned malfunctioning of a circuit or the like. For example, when the battery suffers accidents, such as an accident in which the battery casing is crushed by an external pressure and an accident in which the battery is overcharged by a malfunctioning of a charging circuit or the like, the separator disposed between the cathode and the anode Is broken or melted, causing a short-circuiting between the cathode and the anode in the battery. When the battery suffers an accident in which the battery casing (which serves as an anode) is penetrated with a conductive member, such as a metallic nail or the like, a short-circuiting occurs between the cathode and the iron nail penetrating the casing as the anode. Further, when the battery suffers an accident in which the battery is exposed to heat from an external high-temperature heat source, the separator disposed between the cathode and the anode is melted sooner than the metals used in the cathode and the anode, thereby causing a short-circuiting between the cathode and the anode. With respect to the battery which is in the non-charged state or the completely discharged state, such a battery is free from the above-mentioned disadvantages. However, with respect to the battery which is in the charged state, the above-mentioned advantageous characteristics of the battery (such as high capacity and high voltage) rather adversely affect the safety of the battery. That is, from the viewpoint of safety, the lithium ion secondary battery in the charged state is rather inferior to other types of batteries. The reason for this is considered to be as follows. In a lithium ion secondary battery, as a cathode active material, use is made of a composite metal oxide of lithium, a transition metal and optionally a non-transition metal, such as LiCoO.sub.2. The above-mentioned composite metal oxide used as a cathode active material has a relatively high resistance. Therefore, when the short-circuit current passes through the cathode active material, the temperature of the cathode active material is easily elevated. In addition, when the battery is In the charged state, the composite metal oxide (cathode active material) is in the unstable state in which a certain amount of lithium atoms are liberated from the composite metal oxide In the form of lithium ions. When the temperature of such a cathode active material is elevated, the cathode active material are likely to decompose to generate active oxygen. Therefore, there is a danger that the generated active oxygen vigorously reacts with an aluminum foil (a current collector for the cathode) coated with the cathode active material and/or with an organic solvent used in the non-aqueous electrolyte, thereby rapidly elevating the temperature of the battery.
Therefore, it has been desired to develop a non-aqueous battery exhibiting high safety, in which occurrence of the short-circuiting between the cathode active material and the anode or occurrence of the temperature elevation caused by such a short-circuiting can be suppressed even when the battery suffers accidents, such as an accident in which the battery casing is crushed by an external pressure, an accident in which the battery is overcharged by a malfunctioning of a charging circuit or the like, an accident in which the battery is penetrated with a metallic nail or the like, and an accident in which the battery is exposed to heat from an external high-temperature heat source